The present invention relates to a thermal transfer recording medium and more particularly to a thermal transfer recording medium capable of being used repeatedly at a high density.
The invention described in Japanese Patent Publication Open to Public Inspection No. 68253/1979 (hereinafter referred to as Japanese Patent O.P.I. Publication) has been known as a thermal transfer recording medium for the purpose of multiple usage. In the technology of the aforesaid invention, a finely-porous layer is formed by means of resins and a heat-fusible ink is impregnated in the cavities in the finely-porous layer. However, the density of the dye-transfer-image obtained from the aforesaid technology is low and accordingly high energy is necessary to obtain a dye-transfer-image having a high density. Further, even if it is possible to obtain a dye-transfer-image having a high density through the application of high energy, the edges of the printed image lack sharpness. Technology similar to the foregoing is disclosed in Japanese Patent O.P.I. Publication No. 105579/1980 but the same disadvantages are observed.
In addition to the foregoing, there are known various technologies which provide a thermal transfer recording medium capable of being used repeatedly. For example, a method wherein a vinylmonomer is grafted with carbon black is shown in Japanese Patent O.P.I. Publication No. 185195/1982 and a method wherein an interlayer for the purpose of adhesion is provided between a backing material and an ink layer (heat-fusible coloring agent layer) is shown in Japanese Patent O.P.I. Publication Nos. 36698/1982, 138984/1982, 116193/1983 and 155995/1983 are well-known. In the aforementioned technologies, it is prevented that all of the coloring agents are transferred at the same time when heated by the thermal head and each technology has its advantage to a certain degree but they are not yet sufficient.